In video conference solutions, people at two or more locations can communicate by simultaneous two-way video and audio transmissions. There are different systems through which the participants interact. For example, it can be dedicated systems having all the required components. These systems are typically installed in meeting rooms and auditoriums. There are also desktop systems coupled to or integrated with normal personal computers.
A core technology used in a videoconferencing system is digital compression of audio and video streams in real time. The hardware or software performing the compression is commonly called a codec (coder/decoder). The resulting digital stream is transmitted through a digital network. Other technologies typically required for a videoconferencing system are a video camera or webcam for providing a video input, and a display unit in the form of a computer monitor, television or projector for providing a video output. Microphones are commonly used for audio input and loudspeakers are typically used for audio output. The microphones and loudspeakers are sometimes integrated with the display unit. A data processing unit, e.g. a computer, ties together the components, implements the codec, and maintains a data linkage with other video conference systems via a digital network.
In video switching solutions each participant typically sends several uplink video streams that differ in resolution or other quality aspects. A video switching server selects among the streams received from the main speaker and selects an appropriate stream to send to each receiver in the downlink direction. The downlink streams are selected based on different factors, such as the resolution of the receiver's screen, the bandwidth available in the downlink direction, and the packet loss rate. This means that some of the streams sent by the speaker may be used by many receivers and some streams may not be used by any receivers.
Throughout this specification, a transport path is understood to be a channel suitable for sending video stream data. Thus, an uplink video stream from a sender in a video conference to a video switching server may be sent via a transport path. Similarly, a downlink video stream from a video switching server to a receiver in a video conference may be sent via a transport path. A transport path typically spans over several access technologies, for example radio, as well as some backbone technology, for example fiber.
A participant may experience changes in the transport path, such as a change in the available bandwidth or change in the packet loss rate. The changes in the uplink transport path can typically be due to changes in radio conditions, for example in WiFi and cellular technologies, such as Long-Term Evolution (LTE). The participant can typically adjust the data sent uplink in order to maximize the video quality based on the available bandwidth. The different uplink streams may use separate and independent transport paths, but the more common case is that they share one single, or at least only a few different, transport paths. Thus, a change in the transport path typically impacts multiple uplink streams simultaneously.
The sending participant can typically choose how to distribute transport path resources to the uplink streams. This choice can include everything from impacting all streams sharing the same transport path proportionally to selecting one stream at a time in some priority order to be adjusted before impacting other streams. In the latter case, if the available bandwidth decreases, and if stream bitrate cannot be reduced, one or more of the uplink streams can be stopped. The video switching server can then instead provide the receivers of the stopped streams with another stream of lower resolution, which will decrease the video quality for the affected users. If the available bandwidth increases, a previously stopped uplink stream can be started again.
If the stream bitrate can be reduced in the encoding process, the sender could decide to do that for one or more streams at the event of decreased available uplink bandwidth, meaning that quality is reduced for those streams in a way that depends on the chosen encoding process. Video bitrate can be reduced by decreasing the resolution, frame rate or SNR, and this would of course decrease the quality for the affected receivers.